Gateway 24" LCD Model LP2407

[USchabon]

Re: Gateway 24" LCD Model LP2407

9 PC LCD Monitor
6 LCD Flat Screen TV
20 Desk Top Switching Power Supply
10 Desk Top Power Supply
10 Battery Charger Switching Power Supply for Power Tool
1 Battery Charger Power Tool Power Supply
6 18v Lithium Battery Power Boards for Tool Battery Packs
1 XBox 360 Switching Power Supply and M Board
6 Servo Drives 220/460 3 Phase
1 De-soldering Station Switching Power Supply 1 Power Supply
1 Dell Mother Board
10 Computer Power Supply
1 HP Printer Supply & Control Board


These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

1 Over Head Crane Current Sensing Board
2 Hem Saw Computer Stack Board

All of these had [bad] CAPs POOF
All of the mosfet that are taken out by bad caps [also bad ones]

Could it be a bad mosfet or two that need to be replaced somewhere? I guess we confirmed the power supply is ok with all the readings we gathered, so not there...

But are power supplies the only place where there are mosfets?

[momaka]

Re: Gateway 24" LCD Model LP2407

I "fixed" the cable with a lot of silicone applied in batches, little by little adding all the cables and making sure they weren't going anywhere. I plugged it in and applied a little more silicone to the cable since this will be is resting position. Once it dried up a bit I tested for continuity and I got a solid beep on each cable, between the connector on the power supply and the male connector that is soldered into the LCD inverter.

Sounds more than good enough for testing.

Everything checked out so I went for it and tested with the component out of the TV receiver...

...the menu lights up, but the screen stays full black all the time, through power up and no matter what I do.

What gives now?
...
Could it be that all along it was the backlight that died?

Do you mean that you can see the monitor's menu/OSD controls on the screen? Can you see it well lit? (As if you would on a normally working monitor too?)
If YES, then this is not a backlight issue.

Another way to see if the backlight is working is to go in a dark room and turn on the monitor with a signal. If the monitor LED indicates that the screen is ON, then you should see the backlights in the screen turn ON as well. Even with a black image signal, you can still tell when the backlights are ON, because you should be able to see them "bleed" through the screen.
(If you are not sure what I mean, try putting a black image on a working monitor. Again, do this while in a dark room. Even though the screen is displaying all black, you will see a backlight and/or slight glow from the screen - this is the backlight.)

Feel free to post pictures of what you see as well.

[USchabon]

Re: Gateway 24" LCD Model LP2407

No, the menu buttons are on the bezel. The screen didn't light up at all. I can tell when the backlight is on on this monitor, and it is not on at all. The backlight is not turning on for sure. Don't know if it is because it is dead or because something isn't telling it to turn on, but it is not coming on, with or without signal. Even without signal this monitor would display the logo for a few seconds, and the menu buttons would open the GUI menu which appears on the screen, and neither show up.

[USchabon]

Re: Gateway 24" LCD Model LP2407

Where/how could I get a backlight? I guess I need to open it all the way and test the backlight somehow?

[USchabon]

Re: Gateway 24" LCD Model LP2407

I can't seem to find one, or a used monitor for parts that can be confirmed to have a working backlight... do you guys have any links to sites that might have the part? And does it seem that it must be the backlight or am I wrong to assume that?

[budm]

Re: Gateway 24" LCD Model LP2407

Even if you have one or more bad lamps, the inverter circuit should fire up the lamps then the protection circuit will monitor to see if ALL the lamps start conducting (lamps flash on) and stay conducting, but if the one or more lamps do not stay on within 3seconds then the inverter protection will shutdown the circuit.
So you at least see the lamps flash on for seconds if the inverter board is active.
So what DCV do you have now on the inverter connector? At least one pin should have the 24V, then at least two more pins should have <5VDC (one for bl-on (>2.5V), one for DIM (between 1V or so ~4.5vdc)).
DCV between the two legs of each of the two filter caps that you replaced on the inverter board? 24VDC?

[USchabon]

Re: Gateway 24" LCD Model LP2407

Even if you have one or more bad lamps, the inverter circuit should fire up the lamps then the protection circuit will monitor to see if ALL the lamps start conducting (lamps flash on) and stay conducting, but if the one or more lamps do not stay on within 3seconds then the inverter protection will shutdown the circuit.
So you at least see the lamps flash on for seconds if the inverter board is active.
So what DCV do you have now on the inverter connector? At least one pin should have the 24V, then at least two more pins should have <5VDC (one for bl-on (>2.5V), one for DIM (between 1V or so ~4.5vdc)).
DCV between the two legs of each of the two filter caps that you replaced on the inverter board? 24VDC?

I am having a hard time following your post, but please take a look at these measurements. Maybe the information you are asking me to gather is already here?

Here are the readings for the cable going to what I've been calling the LCD board (the one with the Frankenstein soldering job )

From left to right (moving up towards the LCD board):
1. 0V
2. 0V
3. 0V
4. 5.43V
5. 0V
6. 0V
7. 23.3V
8. 23.3V

Here are the readings for the cable going to what I've been calling the logic board (the one with all the processors and the I/O inputs)
1. 5.43V
2. 5.43V
3. 5.43V
4. 5.43V
5. 0V
6. 0V
7. 0V
8. 0V
9. 0V
10. 0V

Ok, I completely removed the LCD Inverter and the little USB board, I plugged in the logic board to the power board (flipped and on the back of my mouse pad) then I plugged in the power board and took all the same measurements as before:

LCD INVERTER CN ON THE POWER BOARD (left to right towards LCD Inverter):
1. 0V
2. 3.28V
3. 0V
4. 5.18V
5. 0V
6. 0V
7. 25.9V
8. 25.9V

LOGIC BOARD CN ON THE POWER BOARD (starting from the red cable)
1. 5.18V
2. 5.18V
3. 5.18V
4. 5.18V (also red)
5. 0V
6. 0V
7. 0V
8. 0V
9. 3.28V
10. 0V

[budm]

Re: Gateway 24" LCD Model LP2407

LCD INVERTER CN ON THE POWER BOARD (left to right towards LCD Inverter):
1. 0V
2. 3.28V
3. 0V
4. 5.18V
5. 0V
6. 0V
7. 25.9V
8. 25.9V

So how about at the inverter board connector?
Also what DCV do you have between the two legs of the caps you replaced on the inverter board?

[USchabon]

Re: Gateway 24" LCD Model LP2407

With all the boards plugged in and the cable plugged into the wall, I set the multi to 200 VDC and this is what I get on the connector on the LCD Inverter (starting with the red cable):
1. 29.9V
2. 29.9V
3. 0V
4. 0V
5. 4.7V
6. 0V
7. 3.2V
8. 3.2V

Between the legs of the caps I replaced (multi set to 200m VDC) I get 0.02V on both. This is with all boards plugged in and cable plugged into the wall.

I then unplugged the monitor and tested those caps again. The first one started at about 130 (multi set to 200m VCD) and it slowly went down to 0, then I tested the other cap and it said 0.

[budm]

Re: Gateway 24" LCD Model LP2407

Your meter batteries must be low since you are getting 29.9Vdc feeding the inverter board, it should be around 24VDC.
The inverter fuse has to be bad, open circuit, because you are not getting the 24VDC on the two filter caps on the inverter board.

[USchabon]

Re: Gateway 24" LCD Model LP2407

I'll go pick up a new 9V and post the readings again, but it was a new battery when I bought it around 1 month ago or less. Could be a bad one, could have left it on... we'll find out.

What does the inverter's fuse look like? Can it be swapped? Would make sense since the spark that jumped out of the socket when I messed up was about 3 inches long HAHAA

[budm]

Re: Gateway 24" LCD Model LP2407

I'll go pick up a new 9V and post the readings again, but it was a new battery when I bought it around 1 month ago or less. Could be a bad one, could have left it on... we'll find out.

What does the inverter's fuse look like? Can it be swapped? Would make sense since the spark that jumped out of the socket when I messed up was about 3 inches long HAHAA

Fuse (White body with gold ends) designator is F1 as printed on the board right next to the inverter connector.

[USchabon]

Re: Gateway 24" LCD Model LP2407

Fuse (White body with gold ends) designator is F1 as printed on the board right next to the inverter connector.

Cool. How can I make sure I order the right one? And can it be soldered in place?

[budm]

Re: Gateway 24" LCD Model LP2407

Does it show very high resistance? If it does,then you may have done bad power MOSFETs the 8-pin SMD devices, that are shorted out. You will need to get the P/N so you can test the resistance between Source and Drain pins for low resistance readings.

[USchabon]

Re: Gateway 24" LCD Model LP2407

How do I test the resistance for the fuse? If I set the multi to continuity and connect the gold sides and I get nothing

[USchabon]

Re: Gateway 24" LCD Model LP2407

I did the same at all Ohms ranges of the multimeter and got nothing on the fuse when touching both gold ends

[budm]

Re: Gateway 24" LCD Model LP2407

So you have blown fuse, so next thing you need to do is to check resistance between the two legs of those two filter caps to find out if it is showing >10 Ohms, if it does, then it can be solder bridge dues poor soldering works, shorted out power MOSFETs, you need to get the P/N of those MOSFETs.
If they are shown as shorted circuit, then you need to get then new inverter board because I do not believe you can do surface mounted repair.

[USchabon]

Re: Gateway 24" LCD Model LP2407

I set the multi to 20k and I get 2.63 and 2.64 on the caps. Does that mean the MOSFETs are fine because it is less than 10?

[budm]

Re: Gateway 24" LCD Model LP2407

I set the multi to 20k and I get 2.63 and 2.64 on the caps. Does that mean the MOSFETs are fine because it is less than 10?

We are looking for low resistance, so use 200 Ohms RANGE, so 2.63K Ohms mean you do not have shortes between the two legs of the caps.
Right now it does not mean the MOSFETs are not shorted out until you check the resistance between the Source pin and the Drain pins of the MOSFET.

[USchabon]

Re: Gateway 24" LCD Model LP2407

If I check the caps at 200 Ohms I get a 1 (to the left) on both caps.

Which are the MOSFETs, and which are the source and the drain pins? I don't see anything like this on the LCD inverter board. Do you mean on the power supply unit?